This invention relates to electrocardiographic systems and methods, and particularly to a system and method for analyzing the variability in an electrocardiographic signal due to myocardial function, and which attenuates extraneous signal variability. More particularly, the system and method attenuate that portion of extraneous signal variability which is attributable to human breathing functions. The device is useful for non-invasively detecting and analyzing Coronary Artery Disease (CAD) caused by cardiac ischemia.
The resting electrocardiogram (ECG) is a standard test for heart disease. Unfortunately, its sensitivity for detecting coronary artery disease and the complications of CAD is relatively poor.
Scientific studies have shown that the variability of the electrocardiogram signal is a marker for coronary artery disease and its complications. However, to this point it has been impractical to properly measure and analyze this variability in a clinical setting because the patient's breathing causes an even larger level of variability. Breathing causes variability in the electrocardiogram signal due primarily to the changes in the geometry of the chest and tilting of the heart during lung or pulmonary function. Thus, attempts to use the variability of the electrocardiogram signal as a marker for coronary artery disease have met with limited success.
In the past, various methods and devices have been used and proposed to mitigate the effects of breathing. However, these methods and devices have generally proven to be ineffective. One known method of reduction of breathing effects utilizes a computer to repeatedly average a plurality of signal cycles to yield a composite signal which is then displayed for operator diagnosis or is further analyzed by other means. In the process of averaging, the breathing components of each signal cycle are attenuated because they are weaker than the cardiac function components. However, a problem exists in averaging techniques because they mitigate not only breathing effects, but also some low level signals and signal effects which contain relevant electrocardiographic information.
Despite the need for a system and method in the art which detects CAD and its complications by exploiting the relationship of variations in the electrocardiographic signal thereto, and which overcomes the limitations and problems of the prior art, none insofar as is known has been proposed or developed.
Accordingly, it is an object of the present invention to provide a system and method for detecting CAD and its complications in a non-invasive, stress-free manner. It is a further object of the invention to provide a system and method for quantifying and localizing cardiac ischemia.
Another object of this invention is to provide a system and method which detect and analyze variability in the electrocardiographic signal due solely to myocardial function. A further object of the invention is to provide a system and method which reduces or attenuates that portion of the variability of the electrocardiographic signal, obtained in the clinical setting, which is due to repetitive physical changes which occur in the patient's torso, particularly that which is caused by effects of breathing.
Still another object of this invention is to provide a non-invasive, stress-free electrocardiographic analysis system and method which analyzes variations in the electrocardiographic signal caused by myocardial function, without regard to breathing effects, to detect coronary artery disease with a high degree of sensitivity and specificity.